122 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Two spotted mice, each having albinism recessive, must transmit to 

 their albino young, as well as to their pigmented offspring, the character 

 partial pigmentation ; hence an albino of spotted parentage should give 

 only spotted young on being bred to a spotted animal. This supposition 

 the writer has tested and found to be correct. 



It remains to discuss more in detail the relation of total to partial 

 pigmentation. The experiments thus far performed do not show an 

 absolute dominance of either condition over the other, though the tend- 

 ency is in favor of the dominance of total pigmentation in the offspring 

 of a spotted mouse and a mouse unmarked with white, as the following 

 experiments indicate. The writer obtained three young by crossing a 

 spotted black-white mouse (No. 303, Figure 5) with a gray, wholly 

 pigmented house mouse. Two of the young were entirely gray, while 

 the third was gray all over except for a white ring near the tip of the 

 tail. In another case a black-white male was bred to a totally black 

 mouse of house-mouse extraction, and of the three pigmented young 

 obtained all were entirely black, save that the toes were rather lighter 

 colored. They differed in no respect, however, from their mother; In 

 another case a totally gray mouse resulted from the union of a D and a 

 DR gamete, and when bred to an albino of spotted extraction, it gave 

 two plainly spotted and two unicolor young. The result is perhaps 

 similar to that obtained in the cross of the spotted with an albino 

 stock not known to come of spotted parents, for the young tend to be 

 wholly pigmented, though frequently they show a white tip or ring on 

 the tail. Moreover, further intercrossing of these heterozygotes often 

 gave " golden-agouti " and chocolate mice, which show no trace of white, 

 but might have offspring with the white tail tip or forehead stripe. 

 Both Haacke ('95) and von Guaita ('98) speak of obtaining only uni- 

 color mice from their first cross of spotted with albino mice, but Haacke 

 adds that these hybrid animals sometimes showed a fleck of white on 

 forehead or belly. 



Crampe ('85) states that by breeding the wild gray rat (" species ") 

 to the black-white variety, he obtained 4 totally gray animals and 36 

 whirh were gray with white " Abzeichen," in the shape of flecks on 

 the tail, belly, or forehead. By Ititerbreeding these latter, he obtained 

 gray rats and black rats exhibiting all the six classes of coloration which 

 he describes, viz. ; gray, gray with white markings, gray-white, black- 

 white, black wilh white flecks, and black with no markings whatever. 

 The unions of gametes in the first described mating would be 



